<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    html, body {
      height: 100%;
    }
    .container {
      height: 100%;
      display: grid;
      grid-template-columns: 300px auto 300px;
    }
    .left {
      background-color: blue;
    }
    .right {
      background-color: green;
    }
    .mid {
      background-color: red;
    }
  </style>
</head>
<body>
  <div class="container">
    <div class="left"></div>
    <div class="right"></div>
    <div class="mid"></div>
  </div>
</body>
</html>